1. Field of the Invention
This invention concerns the construction and operation of indirect metal extrusion presses.
2. Description of the Prior Art
The characteristic feature of indirect extrusion is that there is no relative movement between the sides of the billet to be extruded, and the walls of the billet container. Consequently, the force required for extrusion is reduced and relatively large billets can be extruded. This however leads to problems if a billet becomes trapped in the container, that is to say, if for any reason the billet cannot be extruded in the normal manner. Removal of a trapped billet is difficult or impossible, as the built-in operating force of the press is in general not enough to expel a relatively long billet, when applied against the high friction between the billet and the internal surface of the billet container. A billet can become trapped ("locked in" or "frozen in"), for example because its temperature has dropped to a level at which it cannot be extruded at the normal high conversion ratio and cannot or ought not to be brought up to a sufficient temperature in the press. A billet may also become trapped for example if the extrusion die breaks.